The present invention generally relates to D.C. commutatorless electric motors, and more particularly to a D.C. commutatorless electric motor designed so that a rotor can be driven smoothly regardless of inconsistencies in the characteristic of rotor position detecting means, and power consumption of switching elements is low.
Generally, a so-called Hall motor employing Hall elements, is widely used as a D.C. commutatorless electric motor. However, as will be described hereinafter in conjunction with the drawings, the conventional Hall motor was disadvantageous in that torque ripple and inconsistent rotation are introduced when the product sensitivities of the Hall elements are unbalanced and results in unstable rotation of the motor. In addition, when there is inconsistency in the temperature coefficient of each of the Hall elements, angles corresponding to intervals in which the coil currents flow become unequal due to change in the ambient temperature, to introduce torque ripple and inconsistent rotation. Furthermore, in the conventional Hall motor, the required total control current for the Hall elements is two times the control current required with respect to one Hall element, because the Hall elements are coupled in parallel with respect to a power source. Accordingly, the power consumption of the conventional Hall motor is high, and is thus unfit for use as a motor of a device which uses a battery as its power source.
In addition, in a record player, for example, there are cases where a record disc is placed onto a turntable which is directly driven and rotated by a phonograph motor, and the rotation of the turntable is interrupted by the operator's hand to clean the surface of the record disc in a state in which a power source is driving the phonograph motor, although this is an undesirable method of operating the record player. In such a case, a rotor of the motor is in a locked state (hereinafter referred to as a rotor lock state), and large currents are applied to power transistors. These large currents applied to the power transistors are exceedingly larger than the currents applied to the power transistors when the rotor is rotating normally, and the collector losses are large. Hence, power transistors having large maximum collector losses had to be used as the power transistors, and the cost of the device became high.